Water-curable support bandages are generally well known in the art. Numerous such bandages are widely available in both tape and sheet form and are typically made from fabric material coated with a water-curable polyurethane resin composition. To use such bandages, the tape or sheet is contacted with water and applied to the injured or diseased part of a patient. The water-curable polyurethane resin composition applied to the fabric reacts with the water and cures or hardens so as to form a substantially rigid member. Such water-curable bandages have many advantages as compared with conventional plaster bandages using plaster of Paris and have been gradually taking the place of the conventional plaster bandages. Since the desirous physical properties and advantages of such bandages are due largely to the polyurethane resin component thereof, substantial research and development efforts have so far been made to improve the polyurethane resin compositions, as a result of which various kinds of such compositions are known at present, some of which are discussed in detail below.
In operation, upon contact with water, the polyurethane resin composition starts a curing reaction, such that the initially flexible water-curable support bandage will also begin to cure and harden. Thus, for instance, after application and of the water-curable supporting bandage to the injured or diseased body part of a patient, after some amount of time, it is no longer able to be rewound if in tape form, and cannot be changed or adjusted if it is in sheet form. As the curing reaction further proceeds, the support bandage comes to have such a strength such that its shape is not changed even if some load is applied to it, and when the curing reaction is completed, the supporting bandage comes to possess a still higher strength. In this regard, one requirement of a water-curable supporting bandage for orthopedic treatment is that it should cure in a short time, so that, in turn, the polyurethane resin composition is required to have a very high reactivity to moisture. On the other hand, it is desirable for the water-curable supporting bandage to possess a storage stability over a long period, such that, while it is preserved or stored, for instance, in a hermetically sealed container, its does not proceed to cure.
As a practical example, the process for applying a water-curable supporting bandage to an injured or diseased part of a patient can include the following steps:
(1) the step of applying the water-curable supporting bandage which is already contacted with water to the diseased body part (the time period available for this will hereinafter be referred to as the "working time");
(2) the step of shaping or modeling, the water-curable supporting bandage which has thus been applied to the diseased part (this time period will hereinafter be referred to as the "modeling time");
(3) the step of maintaining or keeping the thus modeled water-curable supporting bandage until its curing proceeds into the state in which a load can be applied thereto (this time period will hereinafter be referred to as the "weight-bearing time"); and
(4) the step in which the curing of the water-curable supporting bandage further proceeds into a perfectly cured state.
After examining the relationship between the strength of a water-curable supporting bandage which has undergone the above-identified steps and time, the following becomes clear. With regard to step (1), that is, the step of wrapping the water-curable supporting bandage or applying it on the diseased part, if the diseased part has a particularly complicated shape, a certain length of time is required for the application of the water-curable supporting bandage. If, during this period, the curing of the water-curable polyurethane resin composition proceeds too fast and, thus, the water-curable supporting bandage cures too fast, then it can become virtually impossible for the water-curable supporting bandage to be correctly applied in the required position. Therefore, during the shortest possible length of time which is considered to be necessary for applying the water-curable supporting bandage, the strength of the water-curable supporting bandage should desirably be kept as low as possible. For instance, for some applications the working time required should desirably be as short as from about 2.5 minutes to about 3.5 minutes, although such time can vary with the degree of skill of the doctor or technician applying the bandage and the part of the patient's body to which the bandage is applied.
Next, with regard to step (2), in the case wherein the water-curable supporting bandage applied in step (1) requires at least some modeling for proper positioning and supporting the body part, and the strength of the water-curable supporting bandage is maintained at a low value for an excessively long time, then it follows that, even when using some degree of force to model the water-curable supporting bandage to the correct shape, the water-curable supporting bandage may have a tendency to return somewhat to its original shape before it cures sufficiently to retain the modeled shape, due at least in part, to the inherent tendencies of the water-soluble supporting bandage to retain its original shape, and/or the elasticity of the patient's body. When this occurs, too much time and labor can be required for finishing the final modeling of the water-curable supporting bandage. Therefore, it is desirable that, only after the application of the water-curable supporting bandage, the strength thereof should greatly increase.
With regard to step (3), when the modeling is complete, and the water-curable supporting bandage is generally disposed in the correct position, it may still be necessary to keep the diseased part of the patient immovable until the water-curable supporting bandage cures into such a state that an ordinary load can be applied thereto. Therefore, the strength of the water-curable supporting bandage, once modeled, should desirably increase as fast as possible.
Further, with regard to step (4), in order to shorten the time during which both the patient and the doctor must be engaged or involved in the medical treatment, it is desirable for the water-curable supporting bandage to perfectly cure or harden as soon as possible and for the strength of the thus cured supporting bandage to reach the highest possible value. That is, it is ideal for the water-curable supporting bandage to possess such a curing reaction characteristic that the strength of the water-curable supporting bandage can be kept at a low value during the manipulation period during which the water-curable supporting bandage is applied to the diseased part, and then, during the subsequent modeling period, said strength can abruptly increase and keep sharply increasing thereafter to bring the water-curable supporting bandage into a perfectly cured state, thus finally reaching a high strength load bearing capability.